1. Field of the Invention
The present invention relates to a method of test of a clock generation circuit in an electronic device having an external interface and to an electronic device, and in particular relates to a clock generation circuit testing method for an electronic device having a clock generation circuit for an interface faster than the internal clock of the electronic device, and to an electronic device.
2. Description of the Related Art
Magnetic disk devices and other peripheral devices communicate with a host or similar through a prescribed interface. With demands for faster processing in recent years, there have been strong demands for faster interfaces. For example, in high-speed serial transfer over Fibre Channel, SATA (Serial AT Attachment), PCI Express and similar, transfer rates reach 2 GB to 4 GB per second.
In order to accommodate such high-speed interfaces, interface circuits are provided in existing peripheral devices. On the other hand, existing peripheral devices are designed to operate at a prescribed clock frequency, and have an internal clock source. As a result, when equipped with a high-speed interface circuit, it is necessary that the device also be equipped with a high-speed clock source to support this interface.
For example, in an electronic device the internal clock source of which is 40 MHz, a clock source of 75 MHz, 106.25 MHz, or 150 MHz is installed according to the interface speed. Quartz oscillators are used as such a clock source (see for example Japanese Patent Laid-open No. 64-077305).
In such quartz oscillators, depending on the interface, it is required that the oscillation frequency be within 0.01% (for example ±100 ppm) of the specification; but electronic equipment manufacturers install oscillators in peripheral devices and other electronic devices without performing checks of all the clock sources for which a high-precision oscillation frequency is required, opting instead to trust the expertise of the supplier of the clock source. There have been proposals of methods to diagnose problems with a quartz oscillator, when mounted on a printed circuit board, as originating with either the oscillator or the oscillation circuit (see for example Japanese Patent Laid-open No. 9-246868).
However, even among clock sources such as these, the existence of units which do not satisfy specifications cannot be denied. On the part of electronic device manufacturers, tests of individual purchased clock sources would be sufficient, but the installation of dedicated testing tools and equipment by electronic device manufacturers would be a cause of increased costs. Tests of clock source units after mounting on printed circuit boards similarly result in cost increases.
For this reason, after installation in an electronic device (on a printed circuit board), it has not been possible to exclude problematic clock sources until actual faults occur in various tests of the electronic device itself. Moreover, even if problems do not occur in various device tests, there is the possibility that faults may occur in a printed circuit board equipped with a clock source which does not satisfy specifications after the electronic device has been supplied to the market.